When installing, testing, maintaining, or tuning all ranges of fiber optic networks it is necessary to make use of various test sets. A test set ordinarily will include one or more fiber optic jumper cables for verifying the integrity of the signal flow through various parts of a fiber optic circuit. A typical fiber optic jumper cable consist of two standard connectors, connected to a given length of a single simplex cable which is a standard cable manufactured by Dow Corning Corporation. For this application we are using a typical cable consisting of a glass fiber, surrounded by a teflon buffer encased in aramid yarn or kevlar fibers with a PVC outer jacket. The dimensions of the component parts are: glass fiber is 126 μm, teflon buffer is 900 μm, aramid yarn is 1.6 mm, ABS outer jacket is 0.4 mm, and the outside diameter is 2.9 mm. The length of the fiber optic jumper cable depends on the distance that must be spanned by such cable. A fiber optic jumper cable, or simply cable, as that term is used herein, means a light transmitting glass core or fiber encased in a sheath of flexible cladding material which precludes extraneous light collection or loss transversely of the fiber.
A fiber optic jumper cable as currently used for testing purposes in the field normally is accommodated for storage and shipment in a transparent, flimsy, plastic bag. Conventionally, such a cable is wound about a radius of two inches or more to form a coil which is placed in the plastic bag without any additional protection against damage from externally applied forces, such as that resulting from being stepped on or struck by falling objects. The storage of a fiber optic cable in such a bag is undesirable because of the inability to maintain consistent control over minimum bending radii and the susceptibility to damage of such cable while accommodated in such bag.
A fiber optic jumper cable has certain known physical and optical characteristics, such as the fiber, the connector size, and shape, and signal transmissivity attenuating properties of the fiber. These characteristics must be protected carefully during use of a jumper cable. The attenuating properties usually are determined prior to the time the cable is coiled, whereas the coiled diameter of the cable determines the minimum radius about which the cable may be bent or wound to ensure against damaging the glass fiber. These characteristics may be embraced by the term “minimum bending radius” which, as used herein, means the minimum radius about which the cable may be bent without subjecting the fiber to physical damage or any appreciable loss of signal transmissivity.
When a field engineer extracts a coiled fiber optic jumper cable from the plastic bag in which it is stored, it is common practice for the engineer to discard the bag and manually uncoil and recoil the cable prior to and following its use. Manual uncoiling of the cable frequently results in slack lengths of cable and the formation of unnecessary extra coils that may cause the cable to become twisted or kinked, whereas inconsistent control over manual recoiling of the cable subjects it to the possibility that it will be wound about a radius less than the minimum bending radius, thereby physically damaging the fiber and adversely affecting its ability to transmit an optical signal without undue attenuation.
In those instances in which the test set and a fiber optic jumper cable are shipped or stored in the same container, the fiber is exposed to the possibility of being damaged by the test equipment itself during transit.
The distance from the test set to the equipment under test varies in different testing environments. The current practice, therefore, requires the selection of a length of cable which almost always is greater than the distance to be spanned, thereby resulting in excessive sagging and the formation of unnecessary extra coils distributed between the ends of the cable. After use the recoiling of the cable by hand results in uncertain bending radii and increases the risk of damaging the fiber.
The distance from the test set to one part of a circuit to be tested may be, and usually is, different than the distance from the test set to another part of the circuit. One solution to the sagging problem encountered when using a single cable is the use of apparatus disclosed in application Ser. No. 11/081,190 filed Mar. 16, 2005. Such apparatus includes a single cable and two spools about which the single cable is wound. As a consequence the cable must be unwound from and rewound on the two spools in a predetermined order which may not always be convenient.
A principal object of this invention is to provide apparatus which overcomes the objectionable characteristics referred to above.